1. Field of the Invention
The disclosure relates to a lamp assembly and a liquid crystal display device having the same, and more particularly to a lamp assembly for enhancing light efficiency as well as display quality and a liquid crystal display device having the lamp assembly.
2. Description of the Related Art
In general, an information processing device is associated with an interfacing device, such as a display device, for displaying information processed by the information processing device so that users may view images displayed on the display device in accordance with the processed information. Recently, a liquid crystal display (LCD) device is widely used as a display device.
The LCD device displays information by using the optical property of liquid crystal molecules which varies in response to a change in their alignment. In more detail, when electric field is applied to liquid crystal disposed between two transparent substrates, an alignment of the liquid crystal molecules is transformed into other molecular alignment. As a result, the optical property, such as double refractivity, dichroism and light scattering of a liquid crystal cell, is changed, and information can be displayed on an LCD panel by using the change of the optical property of the liquid crystal molecules.
The LCD panel comprises a thin film transistor (TFT) substrate, a color filter substrate opposite to the TFT substrate, and the liquid crystal disposed between the TFT substrate and the color filter substrate. The liquid crystal cannot emit light by itself, but can control transmittance of light incident thereonto. Therefore, the LCD devices using such liquid crystal require light to display images. The light is usually supplied from a separate light source such as a backlight assembly. Consequently, display quality and power consumption of an LCD device having the liquid crystal is mainly influenced by the backlight assembly.
FIG. 1 is a cross sectional view showing a conventional backlight assembly for an LCD device.
Referring to FIG. 1, the conventional backlight assembly 30 includes at least one lamp 10 and lamp reflector 20. The lamp 10 includes a light emitting portion 11, a first electrode 12 and a second electrode 13 formed at both ends of the light emitting portion 11, respectively, and a first electrical wire 14 and a second electrical wire 15 connected to the first and second electrodes 12 and 13, respectively. A first voltage, relatively high voltage, is applied to the first electrode 12 through the first electrical wire 14. A second voltage, relatively low voltage, is applied to the second electrode 13 through the second electrical wire 15. As a result, the lamp 10 radiates light through the light emitting portion 11.
The lamp reflector 20 includes a reflecting layer 21 for reflecting a part of the light proceeding in a first direction to a second direction opposite to the first direction, and a supporting member 22 for supporting the reflecting layer 21 and the lamp 10. Therefore, the lamp reflector 20 improves light efficiency of the lamp 10.
Generally, the reflecting layer 21 is made of polyethylene terephthalate (PET), and the supporting member 22 is made of metal such as aluminum (Al).
However, when the reflecting layer 21 is contacted on an entire surface of the supporting member 22, the heat generated from the lamp 10 due to the current applied to the lamp 10, is transmitted through the reflecting layer 21 to the supporting member 22. Accordingly, luminance saturation time increases due to the heat loss. It takes longer than usual to acquire the maximum luminance of the LCD device.
In addition, a leakage current is generated due to a parasitic capacitance between the supporting member 22 and the lamp 10.
                    C        =                  ɛ          ⁢                                          ⁢                      A            d                                              <Expression  1>            
As shown in Expression 1, the capacitance ‘C’ is generally proportional to an overlapped area ‘A’ between two conductors and a dielectric ratio ‘∈’ of the dielectric substance between the two conductors, and inversely proportional to a distance ‘d’ between the two conductors. Therefore, the parasitic capacitance ‘C’ is proportional to a surface area ‘A’ of the supporting member 22 overlapped with the lamp 10, and inversely proportional to a distance ‘d’ between the lamp 10 and the supporting member 22.
According to a recent LCD technology, the distance between the lamp 10 and the lamp reflector 20 has a tendency to decrease for slimness of the LCD device. The parasitic capacitance between the lamp 10 and the supporting member 22 increases since the distance ‘d’ between the lamp 10 and the supporting member 22 decreases. Therefore, an amount of the leakage current also increases according as the parasitic capacitance increases.
A current supplied to the first electrode 12 is referred as a first current, a current exiting from the second electrode 13 is referred as a second current, and a leakage current leaked from the lamp 10 is referred as, a third current. An amount of the first current is equal to the sum of the second current and the third current. The larger the amount of the third current is, the smaller the amount of the second current is. Use efficiency of the first current may be reduced due to existence of the third current. The leakage current reduces not only the efficiency of the lamp 10 but also overall luminance of the LCD device.
Furthermore, an increase of the leakage current causes an increase of the heat generated from the lamp 10. The heat also deteriorates the liquid crystal and various sheets adjacent to the lamp 10, which also lowers display quality of the LCD device.